text: /*
  @copyright Louis Dionne 2015
  Distributed under the Boost Software License, Version 1.0.
  (See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
   */
  
  #include <boost/hana/concept/constant.hpp>
  #include <boost/hana/concept/integral_constant.hpp>
  #include <boost/hana/core/when.hpp>
  #include <boost/hana/fwd/core/convert.hpp>
  #include <boost/hana/value.hpp>
  namespace hana = boost::hana;
  
  
  // Define a simple model of IntegralConstant
  struct constant_tag { using value_type = int; };
  template <int i>
  struct constant {
      static constexpr int value = i;
      using hana_tag = constant_tag;
  };
  
  namespace boost { namespace hana {
      template <>
      struct IntegralConstant<constant_tag> {
          static constexpr bool value = true;
      };
  
      template <typename From>
      struct to_impl<constant_tag, From, when<IntegralConstant<From>::value>> {
          template <typename N>
          static constexpr auto apply(N const&)
          { return constant<N::value>{}; }
      };
  }}
  
  // Make sure we really satisfy IntegralConstant<>.
  static_assert(hana::IntegralConstant<constant<0>>::value, "");
  static_assert(hana::IntegralConstant<constant<1>>::value, "");
  static_assert(hana::IntegralConstant<constant<2>>::value, "");
  
  // Make sure we're also a model of Constant automatically.
  static_assert(hana::Constant<constant<0>>::value, "");
  static_assert(hana::Constant<constant<1>>::value, "");
  static_assert(hana::Constant<constant<2>>::value, "");
  
  // Make sure we have the hana::value<> function defined automatically.
  static_assert(hana::value<constant<0>>() == 0, "");
  static_assert(hana::value<constant<1>>() == 1, "");
  static_assert(hana::value<constant<2>>() == 2, "");
  static_assert(hana::value<constant<3>>() == 3, "");
  
  
  int main() { }
  